text:
Why are aircraft callsigns pronounced over the radio in a non-phonetic alphabet way?
Why is it numbers are not always pronounced in a phonetic way? For example a flight number of 2390 is pronounced "twenty-three ninety" instead of "two three niner zero"

I thought you were going to ask, why isn't it pronounced two-tree-niner-zero.

What are you basing this off of @Devron? Are you talking about actual ATC communications or announcements?

@GdD I know Civil Air Patrol aircraft use exactly the situation the OP is bringing up. They use "CAP 2390" said "cap twenty-tree ninety" instead of "two-tree-niner-zero".

From actual ATC communications from LiveATC

Callsigns are only there to distinguish - there's usually no CAP20390 AND CAP2390 (which could both be twenty-tree-ninety) in the same airspace. You'll never hear this when a single wrong digit is important, like headings, frequencies etc

@sanchises True. The CAP callsign has only 4 numbers in it read in two-number blocks.

@Devron That is also FAA-land specific. In ICAO-land, it would be Two Tree Niner Zero as you correctly pointed out. At least by the book...

The FAA's ATC orders (section 2-4-20) say that the 'group form' should be used by controllers when talking to any aircraft with an FAA authorized call sign. So you would expect to hear it with airline traffic but not private flights:

Air carrier and other civil aircraft having FAA authorized call signs. State the call sign followed by the flight number in group
  form.

NOTE- “Group form” is the pronunciation of a series of numbers
  as the whole number, or pairs of numbers they represent rather than
  pronouncing each separate digit. The use of group form may, however,
  be negated by four-digit identifiers or the placement of zeros in the
  identifier.
EXAMPLE− “American Fifty−Two.” “Delta One Hundred.” “Eastern
  Metro One Ten.” “General Motors Thirty Fifteen.” “United One Zero
  One.” “Delta Zero One Zero.” “TWA Ten Zero Four.”

Followup question, then: what is the reasoning behind this ATC Order? In what way is Group Form beneficial in this instance, while being undesirable for headings, frequencies, altitudes, etc?

Group form is much shorter to say, taking up less radio traffic.  Also, the exact digits are not important, so long as the aircraft understand "he's talking about me".  With frequencies, headings, altitudes, etc, the exact digits are important.


text:
Why were the cabin lights turned on during the flight?
I was on a flight last night that the Captain came on and said in three minutes we all had to be in seats and buckled due to severe storms we had to fly through. After about five minutes and until we landed-approximately 20 minutes the interior lights were turned on.  This has never happened on a flight I have been on. Was it so we could not see what was going on outside?  There was tons of lightning and clouds.

Probably to make sure your eyes were adjusted to bright light, to prevent temporary flash blindness from the lightning. Read more here: https://en.wikipedia.org/wiki/Flash_blindness

Related question for the opposite (having lights off during takeoff/landing)

I'd guess that to allow cabin crewto act efficiently if bad things happen.

Most likely to keep the passengers awake and alert in the even to severe air turbulence, unusual attitudes, or even a mishap which might be encountered during the passage through those areas of storms.  Awake and alert passengers can better react and avoid injuring themselves and/or others.
It's the nice form of the captain coming on the intercom and saying:
"Good evening ladies and gentlemen.  We are about to pass through an area containing several red cells, possibly hail, and severe turbulence.  If you don't feel like having your head put through an overhead bin, wake up and get those seat belts fastened - NOW!"

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text:
Quadcopter propeller performance
Quadcopters use both direct and contra-rotating propellers to be able to turn and to balance the torque caused by the each of the propellers.
Propeller performance measurement:
When testing the propellers for these quadcopters, why is their performance measured only in one direction of rotation? Would it be useful to test both the right handed and left handed rotations to provide more information to the designer?
Propeller pitch selection:
Why would a designer select a lower pitch to diameter ratio for quadcopters when there are higher and more efficient ratios to choose from?

I am absolutely perplexed by what you are trying to say..."propeller shapes able to turn both directions"? Please explain.

The propellers can turn clockwise and counterclockwise

They may turn in opposite directions more to counter torque than drag. If the props all turned in the same direction it would probably spin around its axis. Having counter-rotating blades means you can turn it left/right using the torque moment of the clockwise or counter clockwise motors.

I understand, but would you need to test this counter rotation for the amount of torque and drag it produces, or would it just have the same and opposite drag when it is spinning clockwise?

The props have to be left handed or right handed, you can't just spin the same prop two different directions and produce lift in the same direction. That being said, there should be no difference aerodynamically from a prop spinning clockwise or counter clockwise if the props produce thrust in the same directions when it spins.

Please clarify what you mean by 'test'.

Also, there are two completely separate questions here, which are related only in that they're both about quadcopter rotors. If you want to ask two separate questions, please make two posts.

I suggested you narrow your question to only one aspect. It is better to ask several precise questions (and if needed adding links into the description) than asking a question whose answer require writing an encyclopedic article.

I edited your post to make the link between the two questions more visible, and adjusted the wording accordingly. I hope I didn't change any how the meaning. Feel free to rollback to your version (and improve it if necessary) by clicking edited <time> ago. The first question is a misunderstanding, but the second is a good one actually.

pitch selection and performance measurement are two distinct questions and I think it should be aksed seperately.

@KaleEvans closing this question is the reason why some of us are attempting to create a new drone-oriented community (Area 51).  I like your question and, from a droner's POV, find it extremely interesting and relevant.  But AVIATION is a community for people who want to be in the air with their gear.  Droners don't want to fly themselves while they drone.  That makes for a difference in perspective which is irreconcillable

@SMSvonderTann please explain why you edit a question and then vote to close it.  Makes no sense, unless you are points farming or unless you suffer from a fractured conscience: vonderTann in the morning, vonderBrandenburg in the evening.  PS: is wiesbaden still a center for camera maintenance?  Took my Arri16 there for maintenance for a decade or two.

When testing the propellers for these quadcopters, would it be useful
  to test both the right handed and left handed rotation of the
  propellers or just one direction?

You may miss something about propellers rotation. A given propeller produces thrust (which is another name for lift) when rotation occurs in the designed direction. When direction is reversed, thrust may be produced, but not efficiently, and will be reversed compared to the regular lift.
A propeller is a wing in rotation. Wings are not used is reverse direction, with a plane going backwards.
Left-handed and right-handed propellers are different:

Thrust is determined in the intended direction of use.

Why would a designer select a lower pitch to diameter ratio

For the same reason than wings on actual planes have an optimized size and incidence. Increasing this size or this incidence is not productive. The limit may come from different reasons, but essentially for weight and drag considerations.
In the quadcopters, the propellers are spun by electric motors that have a limited power and a preferred rotation speed. Propellers are selected to match the rotation speed and available torque of the motor.
In addition turbulence is created by the propeller, especially at high pitch. Turbulence can decrease efficiency of neighboring propellers, so a compromise has to be found between high individual and low overall lift produced.

From Studying the Aerodynamics of Multi-Rotor Drones (Nasa)
Also think about the fact that a propeller just converts a quantity of work (rotation) into another quantity of work (translation of air). The rate of conversion is dependent on the blade pitch. Air translation (lift) can be increased but not beyond the capabilities of the motor to create the equivalent rotation. If this is done, the motor just can't deliver, and it's efficiency decreases (battery will be empty more quickly).

good answer, maybe include a cross section drawing to show that propellers, like wings, are not symmetrical.

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text:
How do I find the serial number and other important information of an old airplane I have?
My dad has passed away and I have his plane. I can't find the paper work but I want to get a replacement title from FAA. Their site says that I need manufacturer name, model designation, N-number, and serial number.  I have the N-number but don't know where to find the other info. Could you please help me find that information?

Is there a packet of paperwork inside the aircraft? Usually there is the airworthyness certificate, registration and manual. Sometimes the manuals also have the serial number on them if they are original. You can also look in the airframe/engine logbooks if you can locate them.

There should be a placard with the serial number on or near a primary structural member, like the wing spar or a firewall. If you can be more detailed about the plane (manufacturer, type), we might be more specific. Please type the N-number into this site and add the information from there to your question.

I will try looking for that primary structure.  The wings are off in the garage.  My mom says she had the paper work somewhere. :( but can't find it.  I did go to that web site and typed in the N number and it came up, "attention, this aircraft's status may not be suitable for operation"  I contacted the number and I got the automated runaround.

If you have trouble finding the paperwork, or if you're not sure what the aircraft is, I suggest you take a couple of photos and add them to your question. That would help us to identify the aircraft type and where the serial number is likely to be.

I have a picture, how do I attach it to this comment?  The N number is 97554

The aircraft is a Stinson 108 (a beautiful airplane when restored). Serial number 108-554. It should also be noted that it is listed as having multiple owners, you may want to try to contact those people. Just use the N-Number look up that @PeterKämpf gave, except under the warning message, click the "continue" link.

oh yes, my mom mentioned something about multiple owners.  hmm.  thanks so much for your help!!!

yes, looked it up, and got all the info

When you finish all the look up can you put all processes you went through as answer? That be helpful to others :)

Do you have the log books for the plane (as you state you dont have the paperwork)? If you intend on bringing this plane back into service or sell it, you will (for all intents and purposes) need the log books along with all the registration documents.

There are three pieces of paper the FAA issues which would fall under the concept of "title" to an aircraft.
The first is an aircraft lien (typically held by a bank when you take out a loan collateralized by the aircraft). This is probably not what you're looking for, but you should inquire as to whether any liens are held against the aircraft before doing any work, just to be sure you have "clear title" to the results of your work.
The second is an Aircraft Registration Certificate - this is a record tying the N number (in your case N97554) to the aircraft itself.
In your case the registration is Revoked, so once reassembled the aircraft would need to be re-registered to be flown. This would be a "Call your local FSDO" situation - Presumably the registration was revoked when the aircraft registry changed to a 3-year expiring registration period.  Also as there are multiple owners listed on the registration re-registering may require more work.
The final piece of paper you need is an Airworthiness Certificate - this should be in the aircraft, and is valid forever. If it's not in the plane you can get a replacement - again, contact your local FSDO.
If you need information you don't have, or want to confirm it before talking to the FAA, look for the aircraft data plate. On Stinson aircraft (going by the N number you provided) the data plate is usually located on the firewall above the copilot rudder pedals as shown here.
On newer metal aircraft it is often located on the tail, under the horizontal stabilizer.
For more information on the aircraft itself check out stinsonflyer.com.

Edit: this question was already answered in the op comments.
Type the N number into the FAA registry here.  It will give you all of the aircraft registration info including the serial number, make, model, and year.


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What is the procedure for an air traffic controller after a major crash or incident occurs on their watch?
How will an air traffic controller will be treated right after a major incident?

I'm not sure if its accurate, but maybe you should watch the moving "Pushing Tin." Its all about that.

Peter Nielsen was murdered by the man who lost his wife and two children in the crash. Really this is kind of broad, because it depends on the circumstances. Anything can happen from nothing, to psychological counseling, to remedial training, to prison depending on the cause of the accident and the controllers involvement in that accident. Sometimes they are immediately suspended, quarantined, and interrogated, possibly within hours of the accident.

@Devil07 Pushing Tin is a horribly inaccurate movie that does not depict reality in any way

The usual advice from the doctor seems appropriate here.

Most units today will have some sort of CISM procedure.

Critical Incident Stress Management (CISM) is the structured assistance for a normal reaction to an abnormal event.
CISM methods are secondary preventive measures which consist of discussions about the incidents in the form of structured individual and group discussions and help the persons affected regain their ability to apply coping strategies. Most of the time these discussions are performed by colleagues who have qualified in CISM programmes (the so-called CISM peer diffusers or CISM peers) or by Mental Health Professionals (MHPs) who are qualified CISM experts. None of the CISM techniques can, or should be, regarded as psycho-therapeutic measures.

Read more at skybrary: https://www.skybrary.aero/index.php/Critical_Incident_Stress_Management_in_ATM


text:
What is minimum information required to identify if two people will be on the same flight?
I asked this question on travel.stackexchange and got an amazing response but I was advised it better suits aviation.stackexchange and should ask here for a better response, so here it is.
I have a set of users and their itinerary details. I want to figure out who all will be sharing a common flight. I do not want to rely too much on the "Departure time" as people could have entered an approximate time into the system. How can I figure this out with minimal information?
Initially, I thought two people with the same flight number and same departure date would be on the same flight. But the same flight can be used again on the same day. Would the combination of "Flight no + departure date + departure city" be enough to identify a unique flight itinerary?
What would be optimal information to identify this?
I also have to keep in mind that there could be people with multiple flights in their itinerary and if at least one flight is common with another passenger, that has to be shown too.

Define "same flight". Same physical airplane? What about codeshares, do those qualify as same flight?

By same flight I mean, same physical flight on at-least a subset of the route. As in, sort of, people should be able to meet each other in the flight.

Yes, Departure City + Flight Number + Departure Date will identify a single flight.
Where you may have a problem is if flight 123 goes from AAA to BBB to CCC to DDD on a particular day, and passenger 1 gets on flight 123 at AAA and flies all three segments, getting off at DDD, while passenger 2 gets on flight 123 at BBB and off at CCC.  To identify that those two are together on flight 123 departing BBB, you'd need to either have passenger 1 enter all the segments of his flight, even though he doesn't change planes at (nor even really much care about) BBB and CCC, or you'd need information about all the flights from some source, so that you know that "flight 123 from AAA to DDD" goes to BBB and CCC in between.

I learned that a flight can have multiple flight number, isn't that true?

@SrujanBarai you may be talking about code sharing which you can find more info on here

Yes so because of codesharing, Ralph's method is not accurate right.


text:
In the US, in a non-emergency situation, can an airplane get a clearance from a tower to take-off or land from or on a taxiway, at their own risk?
In the US, helicopters are cleared to take-off or land on various parts of airport surfaces such as taxiways, grassy areas, ramps, etc. When this occurs the controller tells the helicopter that the take-off is at their own risk. Also, sometimes when runways are closed certain airplanes are sometimes permitted to take off from taxiways as was the case at a local uncontrolled airport recently.
My question is can a pilot of an airplane request from the tower, and can a tower controller give a clearance to the airplane pilot to take off from a taxiway "at their own risk?"  I'm not asking if the controller is required to give the clearance, only if its possible for them to give that clearance if they were so inclined, in the same way they let helicopters take off and land from just about any part of the airport surface. I'm also not talking about emergency situations where an airplane can land anywhere with or without a clearance.

See https://aviation.stackexchange.com/questions/31802/can-planned-runway-closures-prevent-a-plane-from-leaving-an-airport/31814

@EugeneStyer thank you. I did read this one. Maybe I should be asking if there is any regulation against a controller allowing airplane to take off from a taxiway at controlled airports.

I found this local regulation saying that takeoffs from taxiways is prohibited except with special permission. https://codelibrary.amlegal.com/codes/duncanok/latest/duncan_ok/0-0-0-8981

No. FAA Order 7110.65AA provides for such takeoff clearances for helicopters in 3-11-2. Note that "at your own risk" departures are not actually clearances- they are in lieu of clearances:

If takeoff is requested from non−movement areas, an area not authorized for helicopter use, or an area off
the airport, and, in your judgment, the operation appears to be reasonable, use the following phraseology instead
of the takeoff clearance in subparagraph a:
DEPARTURE FROM (requested location) WILL BE AT YOUR OWN RISK (additional instructions, as necessary). USE
CAUTION (if applicable).

You only get "cleared for takeoff" if taking off from movement areas that are authorized for helicopter operations. Note that this may include taxiways, in which case you will hear "Taxiway A, cleared for takeoff" and not "at your own risk." Otherwise you get "at your own risk."
There is no such paragraph for airplanes. The closest is 3-3-2, regarding operations on a closed or unsafe runway. Any aircraft can be given "at your own risk" for landing on a closed or unsafe runway. There is no procedure for airplanes to be allowed to land anywhere besides a runway except for emergency situations.
Taxiways can be temporarily designated as runways, but that's a different situation. If it's being treated as a runway you'll hear "cleared for takeoff" as usual.

I agree that its not a true clearance. But for lack of a better term, lets called it a "clearance" at your own risk, because they are looking at other traffic in the area before they "clear" helicopters to take off from the ramp at their own risk.  Our department was allowed to takeoff from taxiway during a period where the runway was closed. It wasn't an emergency, but it was interesting, and got me thinking about it.  I'm going to call and ask the guys at my tower and report back.

@Devil07 Don't call it a clearance because it's not a clearance. If you heard "cleared for takeoff" on a taxiway then it's possible the taxiway was temporarily designated as a runway.

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text:
Did the FAA used to require pilots to have valid sectional for VFR cross country flights?
Did there used to be an FAR in the 1990ies that required VFR pilots to have in their possession a valid sectional for cross country flights? I seem to remember this rule from before 2000, but can't find any such rule in the FARs today.

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text:
How many active pilots are there in the US? How many are women?
How many active pilots are there in the US?  Also, how many active flight instructors are there?  Out of all of active pilots and flight instructors how many are women?

According to the FAA, as of December 31, 2016, there are:
584,361 Active pilots (39,187 are Women pilots, or about 7%)
104,382 Flight Instructors (6,848 are Women Flight Instructors, or about 7%)
The ratio of female instructors to female active pilots is virtually the same as for males.

It's interesting that the percentage of active pilots who are women and flight instructors who are women stay the same.  I wonder if that's true of women in most highly-skilled highly-certified technical fields.


text:
Any FAA or other regulations prohibiting taxiing between parked aircraft?
So the other day I was getting checked out at a local FBO, after returning to the ramp, instructor told me to taxi between two parked (tied-down aircraft). It was a tight squeeze but I taxied at about 1 MPH and I looked at left wing while instructor kept an eye on right wing. I really didn't think anything of it. Note, access to the other side of the line was blocked off by some vehicles so we couldn't taxi in from the back, hence cutting between two parked aircraft. However, we could have shut down on the front and pushed the aircraft back into its parking spot.
However, about 5 minutes later, a car drove up to us as we were securing the aircraft. It was the owner of one of the aircraft that we taxied next to. He spoke to the instructor, I didn't hear exactly what he said, but it was something about not taxing so close to his aircraft. Personally, I have no problem, pushing the airplane back into its spot, but it got me thinking about what regulation if any is implicated here.
I looked, and didn't find anything. So my question is whether there are any FAA, airport or other regulations or rules that prevent a small aircraft from taxiing between two parked aircraft on the ramp? I don't think there is any legal authority prohibiting taxiing between aircraft, or how many feet you must keep from a parked aircraft.
This reminds me of the aviation joke:
Aircraft Squawk - Left main almost needs to be replaced.
A&P Response - Almost replaced left main.
In this case:
Aircraft owner - You almost hit my airplane.
Me - You're welcome.

I don't believe there is any regulation for this on the FAA side. Just look at how close airliners get while taxiing around gates/push-back. Airlines may have company policies or airports may have policies, but that would be too broad to answer here (and you are asking about GA or small aircraft).

How about "careless or reckless such as to endanger the life or property of another", or however exactly the regulation goes? Though I would argue you were likely neither careless nor reckless, but rather aware of the danger and taking appropriate steps to mitigate it, assuming of course that really nothing got damaged or hit. But next time, yeah, I'd suggest considering to just move the aircraft by hand power instead...

@MichaelKjörling  I agree that is the only possible one that might apply. Although, like you said, with power at idle, riding the brakes at a crawl probably doesn't meet the level of careless or reckless. :)

Also, I think it was an airplane that usually lives in a hanger; it was shinier than the tie-down riffraff.

There isn't any such regulation.  That part of the airport is a "non movement area" (if you want a reference).  Of course, you want to be a good neighbor, and not toss rocks, etc.  I usually push my airplane into parking, and pull it out before engine start.  But that is just me.

I totally agree! I rent so usually all of the aircraft in and around the rental aircraft are the FBO's aircraft, and they don't have a problem with us starting up on the line. Personally, I usually taxi to the parking spot and push back unless its clear. However, I can also understand that instructors who are doing this 5-6 times a day are in a bit of a hurry and want to taxi through into their spot. But Its definitely a "being a good neighbor" issue more than a regulatory one.

The non-movement area is still governed by 91.13. The movement area is defined as the area of the airport used by aircraft for taxiing, etc, "exclusive of loading ramps and parking areas;" 91.13 (b) applies to "any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo)."

This operation may be governed by 14 CFR 91.111:

(a) No person may operate an aircraft so close to another aircraft as to create a collision hazard.

The question is whether taxiing an aircraft under its own power counts as "operating" that aircraft:

Operate, with respect to aircraft, means use, cause to use or authorize to use aircraft, for the purpose (except as provided in § 91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner, lessee, or otherwise).

In other words, whether or not taxiing an aircraft at the end of a flight is using it "for the purpose of air navigation." I am not a lawyer but I imagine it would not be difficult to argue that taxiing post-flight falls under the umbrella of "air navigation."
Regardless, 91.13 would apply (see how they strip the "air navigation" definition out of the term "operate"):

(b) Aircraft operations other than for the purpose of air navigation.  No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.

That definition—"used for receiving or discharging"—refers specifically to the non-movement area of an airport. Just because you are operating on the non-movement area does not relieve you from the regulation. However, now a violation depends on whether you were "careless or reckless."

That's a fair point. But I would say that if a Part 135 or even Part 91K aircraft has ever or could ever use that ramp, then it is a part of the airport used for air commerce. (And that's without trying to parse whether "used for air commerce" describes the part of the airport specifically, or the entire airport in general!)

I think a weakness in this approach is the lack of demonstrable collision hazard. It wasn't luck which kept a collision from happening, it was proper care and operation. Reasonable minds might disagree on how close you have to get before crossing that line to "hazard", but I would suspect that for any punitive administrative action to hold there would have to be some component of the operation which was not in the pilot's control. For instance, if it were gusty, the wings were rocking back and forth, and it was just luck that they didn't make contact.

@Kenn, I'm not claiming that this definitely was or wasn't a violation of 91.111—just pointing OP to a potentially-relevant regulation.


text:
Why don't airbus aircraft have raked wingtips?
Most airbus aircraft have sharkfin winglets or blended winglets. Why is it that none of them have raked wingtips like the 777-300ER?

Probably because Boeing holds a number of patents related to raked wingtips, like US5039032 A High taper wing tip extension and US6089502 A Blunt-leading-edge raked wingtips, among others.

The first of those two patents is expired; the second will expire about a year from now.


text:
What exactly did this mechanic sabotage on the American Airlines 737, and how dangerous was it?
An American Airlines mechanic sabotaged a 737 in Miami

An American Airlines mechanic accused of sabotaging a navigation system on a flight with 150 people aboard at Miami International Airport was denied bond by a federal judge on Wednesday after prosecutors suggested he may have links to a Middle East terrorist organization.
Abdul-Majeed Marouf Ahmed Alani, a 60-year-old veteran employee, told investigators after his arrest earlier this month that he disabled the system because he was upset over stalled union contract negotiations with the airline and wanted to generate some overtime for maintenance on the plane. He said he meant no harm to anyone, and the July 17 flight was aborted before takeoff after an error alert appeared on the navigation system.

His defense attorney said it wasn't as big a deal as they were making it out to be

But Alani’s assistant federal public defender, Christian Dunham, said the prosecutors were exaggerating the evidence. He pointed out that there was a second navigation system still working on the plane so his alleged sabotage could not have caused it to crash.
“We don’t believe he intentionally endangered the safety of people” on that flight, said Dunham, who sought a pretrial bond signed by Alani’s family members in California and Florida. “I think the government is blowing this out of proportion.”

What was it he sabotaged, and how serious would it have been if it had taken off?

I'm not experienced enough to answer this formally but the assertion by the defendants lawyer that "there was another system" is absurd and dangerous. They went from two systems to one. That reduces the margin of error and is still dangerous. I don't quite know the stats and the lingo here, can an answer include some remarks on this?

Couldn't agree more with @Freiheit.  Everyone deserves a defense; the public defender in question should be given a medal for the most astonishing, astounding, spectacular line of b/s of the year.

@Freiheit Assuming the mechanic had the opportunity to disable both systems, the fact that he only disabled one could indicate his intent wasn't to make the plane crash.

It's a serious crime, but what that guy did, only affecting one system out of three, would be unlikely to cause a crash if the pilots were half way reasonably competent.  The take-off would be rejected as soon as the blocked side's speed tape failed to "come alive", well below 80kt (the pilot not flying checks that both speed tapes start to move as the airplane accelerates - this would be the first obvious clue and is a very basic action on a jet).

In fact, the article quoted in the question says that the takeoff was aborted because the damage was detected.

It actually says the flight was aborted before takeoff.  That's different from the takeoff was aborted, and could be also interpreted as cancelled..

I downvoted because the statement "would be unlikely to cause a crash if the pilots were half way reasonably competent" is overly judgmental and I think, incorrect.  Unreliable airspeed in flight is a serious problem, and not terribly easy to deal with.  I agree with you that it shouldn't cause a crash, but it has caused crashes in the past.  Further, the idea that "if they accelerate to 80, detect a mismatch, and abort, it's safe" is also wrong, aborts above 80 kias are considered high speed, and are not only moderately dangerous, but also often result in damage to the aircraft.

@nexus_2006  I said "well below 80kt" (or 90 or whatever)  The tape moves long before 80kt so it would be a low energy reject.  It's something that's done regularly in the sim on recurrent.  Verifying speed alive, on BOTH sides, is Job #2 for the pilot monitoring after verifying engine parameters after thrust set. Now, if the PNF wasn't, you know, doing his/her job and paying attention, and called airspeed dead just before V1, well we're back to the halfway competent thing aren't we.

In several news reports, Alani claimed to have verified that his sabotage set off an indicator inside the cockpit (which he claims was his actual goal). If true, he had to have done something more than just plugging up a pitot tube.

It's utterly astounding to try to "softly defend" some fool who turned off a major system on an airliner.

What on earth are you talking about?


text:
Why do different aircraft have different maximum operating temperatures?
I was reading this Wired article about the recent Phoenix heat grounding some jets. It's a great read on why heat is detrimental to lift, but it raises a point it never answers (emphasis mine)

Phoenix just provided another reason to hate flying: the heat. With temperatures there expected to hit 119 degrees Fahrenheit, airlines canceled more than 40 flights today.
Wait. What? Airplanes can't fly because it's too hot? That's crazy.
No, not really. According to news reports, the heat poses a particular problem for the Bombardier CRJ airliners, which have a maximum operating temperature of 118 degrees. Bigger planes from Airbus and Boeing can handle 126 degrees or so.

Is this solely due to the size of the aircraft, or is it a difference of manufacturer?

related: https://aviation.stackexchange.com/q/29671/1467

There are a few different things going on here. For the best answer, see this blog post.
To summarize his points, there's a combination of factors:

The Bombardiers simply aren't certified at those temperatures.
Their combination of small wings and small jet engines makes high temperatures particularly problematic for them. With the air density decreasing as the temperature rises the wings get less lift and the engines suck in less oxygen. The bigger jets have larger wings and bigger engines which make up for their larger weight so they can fly while the regional jets can't.

So to answer your question ("Is this solely due to the size of the aircraft, or is it a difference of manufacturer?"): Yes


text:
The condition that wind would effect indicated airspeed
What is the one condition that wind does effects our indicated airspeed?

Can you be more specific? There is no one such condition, but rather many.

If your question is "does wind variations affect indicated airspeed in flight?" then yes, but only momentarily due to the aircraft inertia. The aircraft tends to remain at the same groundspeed while its speed relative to the wind has changed. However it quickly gains or loses groundspeed to mach the same previous IAS as engines can create only a move which is relative to the ambient air speed (via propeller or jet).

There are many, but most obvious is when the aircraft is on the ground.


text:
How does the US space shuttle control pitch when landing without a canard?
Looking at the design of the US space shuttle, I'm curious to understand how it's able to control pitch during landing? By just looking at the design, it appears that it would need some kind of canard to control the pitch, but I don't see one on it.

The shuttle, like other delta-wing aircraft before it, have their ailerons located far aft of the CG.  (There are many examples of delta wings).  In that aft position they can fulfill the dual role of ailerons (deploying opposite each other to cause roll) and move up/down together to cause pitch changes.  Thus the term "elevon" is used to denote their dual role.  Most often this means (a) using spoilers to augment roll authority, and (b) high landing speeds because trailing edge flaps would cause a nose-down pitch input.

Your motto is really nice "Never memorize something that you can look up on stackoverflow.com": apparently you didn't apply it before asking this question :)

@sophit I did, and Google too, but didn't find the answer I was looking for. A site I came across described using thrusters to control pitch in space but not while landing.

It had elevons...why would it need a canard?

Ah ok. Hopefully the other answer answers your question.

@MaxR, OK if I copy/paste your comment into an answer?  ;)

When you look at a shot of a shuttle landing, there is almost no nose-up elevon displacement to hold the nose up during the flare. I'm wondering if most of the pitch up force to maintain the landing attitude is coming from the drag of the split rudder, being well above center of mass.

@MichaelHall Absolutely.  It’s marked as duplicate, so I can’t.


text:
Are pilots in a jetliner allowed to swap seats?
I just watched a video about the crash of Air India Express flight 1344

Part of the reason for the crash was apparently, that only the captain was allowed to land the plane on this airport and that the windscreen wiper on the captain's side failed, so he had reduced visibility.
Would it be allowed for the captain and the first officer to swap their seats, so that the captain can still land the plane with a working windscreen wiper?
(I know, this wasn't the only reason for the crash, just wondering in general.)

Usually, this would not be permitted by the airline. First officers (FOs) are trained to fly from the right-hand side and captains are usually only trained to fly from the left-hand side. The captain may previously have been an FO on this aircraft type (possibly long ago), but could also have become a captain on another type and then transitioned, so they may have no experience flying this type from the right.
The only exception here is a line training captain. These captains are specifically trained to fly from both sides because they also do line checks of other captains (and therefore have to sit on the right during such checks). But even then, the FO would not be trained to fly (or even just monitor) from the left-hand seat. Therefore, for normal operations the answer is clearly no.
However, you are asking about an emergency. If the captain thinks the only way to safely land the plane is to switch seats, then they are allowed to do it. This kind of discretion is typically allowed in an emergency, e.g. in Europe:

NCO.GEN.105 Pilot-in-command responsibilities and authority
(e) The pilot-in-command shall, in an emergency situation that requires immediate decision and action, take any action he/she considers necessary under the circumstances in accordance with 7.d of Annex IV to Regulation (EC) No 216/2008. In such cases he/she may deviate from rules, operational procedures and methods in the interest of safety.

(EASA Easy Access Rules for Air Operations)
Whether switching seats is actually helpful in the situation you described really depends on the details of the situation. How experienced is the captain flying from the right-hand side? If they have never flown this type from the right, I doubt switching sides would improve safety. How much experience does the FO have? If the captain trusts the FO to do the landing, despite flying into a captain-only airport, it might be better to let the FO fly.

Yeah, having to deal with the fall-out of letting the FO land the plane when he shouldn't have is a much better option than being dead.

Thanks for the detailed answer! In the situation of the video, the broken wiper wasn't the only or even the main reason for the crash, but in other situations something broken on the captain's side might be (e.g. broken controls or instrument displays). I didn't consider how asymmetric a jetliner's cockpit is. I've only ever been in the cockpit of a tiny 5-seater, and there the controls were almost symmetrical. Didn't know that the pilots were trained that much towards using just one side of the plane.

@FreeMan Yes, being dead isn't helpful for the career either^^

I don't know the circumstances related to this particular crash. And, I have never flown anything bigger than a small turboprop. However, I have flown in some pretty horrendous weather and the wipers help, but not that much.
I wonder if the nose-wheel steering control on the captain's side might be a good reason for the captain to keep his normal seat.

Nose wheel steering is also controlled via the rudder pedals (up to 7° on the B737). You wouldn't use the tiller during takeoff and landing. You switch to the tiller once slowed down to taxi speed.

Thanks for that clarification. It is something that I have always wondered about.

There's no law against swapping seats as far as I know, but it isn't advisable. The location of switches, controls and instruments is different to each position, and training is specific to those positions so that the knowledge is ingrained. If the captain and first officer switched positions both would be unfamiliar with the positions of some controls and would be using the opposite hands to control stick and throttle, which would be a much higher risk than a broken wiper. You don't want the handling pilot to forget where the flaps are on a bad weather approach!

I must say I disagree with the assertion that switching seats would confuse the pilots with regards to the controls. Basic flying is basig flying, regardless of on which side certain controls are, and since pilots in general are a pretty carefully selected bunch of people with above average capabilities, adapting to "new" surroundings should not be a problem as long as it's done in haste.

Airliners are anything but basic @Jpe61. Cockpit familiarization is a big part of training, this is so pilots aren't hunting around for switches.

I'm not saying airliners are basic. I'm saying professional pilots will be able to maintain mental mapping of switches regardless of the seat they are occupying. Basic flying such as final approach and landing is not cluttered with throwing swithces in haste. At least it should not be.

Someone can't have a mental map of switches for a position they've never occupied.

@Jpe61, this  is a similar question and the answers agree with my position. https://aviation.stackexchange.com/questions/61026/if-the-captains-screens-are-out-does-he-switch-seats-with-the-co-pilot

@GdD, first, there are exceptions, but most captains have considerable time as a first officer in the right seat of their equipment.  Second, what switches do you think the pilot flying needs to switch once configured for landing and on a stabilized approach?

Switching seats IS a big deal in a modern airliner. To say otherwise shows you have never done it.

Lost in this is the difference between two situations.  In normal flight operations a crew should NOT ever be depending on muscle memory and blindly reaching for a configuration item.  Config changes should be more deliberate—announce, look, touch.  But in an emergency, the crew may have to rely on rote/muscle memory, so there could be a downside to swapping.  But crisis impairs our fine motor skills significantly, thus looking becomes more important.  If this was US/NTSB, one branch of investigation would be how a procedure came to require the captain to be the flying pilot.

@GdD both answers agree that places are not switched, one speculates that viewpoint is different and controls may be confusing in an emergency. I agree that switching seats is a bad idea, and iirc it is prohibited, not as such but via other regulation, I'll dig it up. I do not agree that switching sides would be confusing.

Even if you did transition from the right seat to the left seat, on the same aircraft, it only takes a short time before you forget the “flows” from the other seat. When placed in the wrong seat at short notice, your brain turns to mush and your hands reach for the wrong spot on panel. Captains reach up with their right hand while FOs reach up with their left hand. Switch seats and watch them fumble around.

At most operators, Pilot In Command flying from the right side requires an internal certification or qualification as a Training Captain if the other pilot is an FO.  If the PIC doesn't have that, they will be very reluctant to fly right side as PIC. At the private operator I flew RJs at as an FO, all the Capts were Training Capts, and almost all my flying when I was PF was from the left seat. My sim training was half left seat half right seat.  I only ever landed a live airplane from the right seat a few times.


text:
How does a fan differ from a propeller?
Why is the fan in a turbofan different than a propeller in a small airplane? Why do propellers typically have 2 or 3 blades, but the fan has a lot more? And why is the fan shrouded but the propeller open?
I read that a ducted fan is more efficient at very slow speeds (it generates more static thrust than an open prop), but at high speeds the drag becomes too great and you're better off with an open propeller. Which is why they use a ducted fan in hovercrafts, for instance. But if that's true, shouldn't the fan in a turbofan be open (unshrouded), considering the high speeds (higher than a propeller)?
Also, how does the fan get away with supersonic tip speeds and the prop don't? Would the fan be more efficient if tip speeds were lower?

Related

Also related: Why don't aeroplanes use propellers with more blades like the intake on a fanjet?

The simple answer that covers the majority of engines is that a fan has a shroud. The possible exception are unducted fans or Open Rotor Engines, which are a hybrid between a turboprop and a fan engine.
A more scientific answer is based on the difference in disk loading: How much power per disk area can be pumped into the fan for propulsion. For propellers, this is distinctively less than for fans. Some examples:

Cessna 172 with O-320 engine (150 hp) and McCauley 1C160 prop (1.9 m diameter): 39.45 kW/m².
P-51D with Packard-Merlin 1650 (1590 hp) and Hamilton-Standard prop (3.4 m diameter): 130.59 kW/m².
Lockheed C-130H Hercules with Allison T-56 engine (4590 hp) and Aeroproducts propeller (4.1 m diameter): 259.25 kW/m².

With jets, this comparison needs power when thrust is listed. Therefore, we make the heroic assumption that the speed at the fan is Mach 0.4 in static conditions and thrust is split according to bypass ratio (which is completely imprecise but will do for the purpose here):

BAe 146 with Lycoming ALF 502 (31 kN static thrust, 5.7:1 bypass ratio and 1.02 m fan diameter): 4254.35 kW/m².
Boeing 747-200 with Pratt & Whitney JT9D (213 kN static thrust, 5:1 bypass ratio and 2.34 m fan diameter): 5388.74 kW/m².
Boeing 777 with GE90 (388.8 kN thrust at take-off, 8.4:1 bypass ratio and 3.124 m fan diameter): 6077.23 kW/m².

I guess by now you see where this is heading: Turbofans are simply a different class when thrust per frontal area is concerned. And for this to be possible, three conditions must be met:

A well-designed intake which produces uniform flow over the engine face. The shroud is only the consequence of providing the fan with an intake.
A high solidity factor of the fan/propeller (the ratio of the total blade area of the propeller to the disk swept out when the prop turns)
High dynamic pressure at the engine face, so the engine power can be absorbed by the fan/propeller.

Note that those conditions depend on each other: Without the solidity, much less power could be absorbed. Without the intake, the supersonic flow at the fan tips would produce horrible losses and noise.
Now for the crazy ones. The misfits. The rebels. The troublemakers. The round pegs in the square holes:

Antonov 70 with Progress D-27 (14,000 hp and 4.5 m prop diameter): 656.4 kW/m².
MD-81 with GE36 UDF (6661 kN thrust at max climb and 3.25 m prop diameter): 803 kW/m².

Here it is hard to make a clear call whether these are fans or propellers. Their proper name "propfans" hints at that already.
A last word on terminology
Efficiency is a measure how much effort is needed for a certain result. An efficient prop needs less power per unit of thrust produced. It has few blades, turns slowly and has a big diameter. A subsonic fan would be more efficient, but would create much less thrust for a given size.
If you want to express the capacity for thrust creation at a specific diameter, use disk loading, not efficiency.

So the shroud is basically an aerodynamic complement to the fan intake? But also, I was under the impression that the fan acts a little like a compressor, that raises the pressure of the air and then the air is ejected at a higher speed than the intake speed. I say this because of the nacelle shape. The exit usually has a small diameter, which to me looks like a convergent nozzle. I know the jet core uses this principle, but does it apply, to a smaller extent, to the cold flow of the fan as well, or is the shroud merely to control the intake flow? thanks

@Anonymous; You are right, the flow contracts while being accelerated. See this answer for a propeller, where the same happens, just without a wall between inner and outer flow. The shroud just follows the streamline contour.

OK, @PeterKämpf, can you please be consistent in your usage of fractional notation? For props and kW/m², you use the American decimal to differentiate the meters from fractions thereof 1C160 prop (1.9 m diameter) and 4254.35 kW/m², yet you use the European comma for jets 3,124 m fan diameter. It took a moment to wrap my head around just how huge that fan was, then to realize you switched methods on me.  :)

@FreeMan: Sorry, that one slipped through. I did the list by copy and paste and did not look at the decimal point. Thank you for catching it!

I figured that was probably a copy/pasta issue. It did really throw me for a minute, though! Your answers are so good, it's fun to realize you're just human like the rest of us.  ;)

@FreeMan: Thanks. Did you catch the Easter egg? (Hint: It's a quote from a commercial ...)

@fooot: Are the nonbreaking spaces messing up the layout? I tried to avoid splitting the lines between number and unit. Please help me what caused you to edit the post - for me I see no difference.

I'd guess it's the Now for the crazy ones..., but I don't watch a whole lot of commercial TV.

I downvoted this because I think "prop" came from the early colloquial by someone like Wright or Curtiss. And when they decided to name the device we now call a "turbofan", they didn't sit down and measure the disc loading, check to see if it exceeded some prop/fan discrimination line, and decided to call it a "fan". They looked at the thing and said, huh, it looks more like a fan than a prop.

@rbp: Did you consider that I tried to answer the question? And, by the way, the word propeller was used long before Curtiss or Wright.

@FreeMan: Yes, and this one has its own Wikipedia page.

@PeterKämpf yes I did consider it. But I think you are reverse engineering an answer based on observed properties, with exceptions that don't fit the rule you set out. I don't think the word "prop" was used in the context of aviation before Wright, which is the topic at hand, and I eluded to that when I spoke of the term coming from Mariners.

@FreeMan Now I want to see that 3.124 km fan. - lol - The fan diameter would be longer than most runways.

You and me both, @reirab, you and me both...  :)

@FreeMan To keep the tips subsonic, its maximum rotational speed would be about 2 rpm. - lol

First, let's start with the simplest machine, the screw, which converts rotational motion to linear motion.
A fan is a screw whose primary purpose is to move the fluid (air for a plane or water for a boat) which surrounds it.
A propeller is a screw whose primary purpose is to move (propel) the object that it is attached to, such as a boat or a prop plane. And indeed, mariners use the term screw instead of prop.
In the case of turboprop and turbofan, the turboprop uses its prop as the primary means of motion, whereas in the turbofan, the fan simply increases the velocity of the air, but doesn't provide the primary means of motion for the aircraft.

the gasses expelled by the turbine itself

now we're getting into etymology. when the word turbofan was devised, there were only low-bypass ratio fans and the exhaust gasses provided the primary means of propulsion. even as high-bypass fans were developed, the name stuck.

feel free to upvote, then :)

That's correct in the case of the low BPR engines, but not in today's civil engines for fuel efficiency purpose, as explained here: What is the bypass air in a turbofan engine actually for?

Yes and I'm saying (again) that turbofan is a historical term given to the LBPR engines, when the gassed not the bypass air provided most of the propulsion. The name stuck, even though most of the thrust is now produced  by bypass air in HBPR engines.

the fan simply increases the velocity of the air I'm not sure what you're saying with this. It is providing motion for the aircraft. Maybe in LBP it's not the primary means, but it is still performing the same function as a propeller.

Between this answer and your comments on Peter's answer it seems you're pointing out that prop vs. fan is a continuum, which is true. But other than the propfans Peter mentions there are distinct differences between props and fans used today. That what the question is about, not the difference in terminology

In simple terms, the working principle is different:
A propeller is a rotating wing. This means that its main working principle is the Bernoulli principle. A difference in pressures (i.e. low pressure in the front and high pressure in the back) causes the plane to move forward. Is the same as in the helicopter rotors. See https://en.wikipedia.org/wiki/Lift_(force) and https://en.wikipedia.org/wiki/Airfoil
The turbofan is mainly a reactor. This means that its main working principle is Newton's third law. The high velocity air that is forced trough the nozzle pushes the plane forward. The same as in a garden hose. See https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion
To answer one of your additional questions, the one that is less efficient at high velocities is the propeller. This is because, in the propeller, at high velocities the air is flowing from the front to the back causing the pressure to rise at the front thus stalling the propeller.
In the other hand in the turbofan, the additional pressure at the front actually helps the air to be forced trough the nozzle increasing performance.
At extremely high velocities, however, the drag from the fan becomes very high and the speed is limited again (but at a higher velocity than in the propeller.) To achieve even more velocity, the rotating blades are removed and the air is forced trough the compressor because of the very high pressure at the front (See ramjets.) The working principle of ramjet is also Newton's third law.

@SMSvonderTann, A turbofan is a ducted fan and is clearly the kind of ducted fan the OP is about.

No, the principle is not different. Propeller and fan (turbocompressor) are both rotating wings. A pressure difference is the only way to make air apply force on anything, so they both use that too. And they also both use air as reaction mass, because one simply can't work around the laws of motion.

You're right indeed Jan. All laws of physics are present in both devices. The difference is that, by design, the main principle is different. For example, in the propeller, the air trough the blades comes mainly from  the sides (not from the front.) For this reason, in propellers, Venturi effect is more important than Newtonw's third law. In the other hand, in the turbofan, the air behind the blades is compressed and accelerated before leaving the nozzle, making Newton's third law to having a greater impact than Venturi effect.

I think you have a point, Krauss, because props practical limit seems to be around 700km/h, they can't push air at faster airspeeds. Turbofans, however, cruise at 900km/h, so they must be doing something different from propellers. Apparently they act more like compressors.

First of all, the Venturi effect is specific to enclosed structures, like a pipe. I think you are referring to the Bernoulli principal. I second JanHudec. Both propellers and fan blades use the exact same method of reducing pressure to accelerate air. The Newtonian reaction force is the result of accelerating that air. There's no order of importance. The more Bernoulli you have, the more Newton you have.

You're right Tom. It's my mistake. I should have said Bernoulli principle instead of Venturi. I also agree that the explanation I offer could be overly simplistic but the point is (as I explained before) even though all laws of physics contribute to build the thrust force, the design differences takes advantage of different principles. Note: Thank you for the correction I'm editing the answer.

@Anonymous: What is different is the intake. It slows down the air in case of the fan, so it never "sees" the actual flight speed.

I guess both the propeller and the fan act in the principle of conservation of momentum, call it 'action-reaction', it send backwards a mass of air that pushes the device forward, the speed of expelled air mass, and the airspeed of airplane have an influence on which type of propulsive method gives better results, a lot of air at a not very high speed, or a lesser mass of air expelled very fast.
German engineers during WW II thought that propellers would be good up to a bit above Mach 1, but the contra-rotating propellers version of the F-84 Thunderstreak jet fighter proved so noisy that those close to the running engine or airstrip got sick. Here is a brief YouTube audio recording of the F-84H 'Thunderscreech':

You may like the attached chart, from the booklet: 'Ducted Fans for Ultralight Aircraft', by R. W. Hovey. It shows the efficiency of different propulsion systems according to AirSpeed of a flying machine.
Typical Propulsion systems efficiency
There's a more detailed analysis of the subject in a 2009 Thesis by Leighton Montgomery Myers, Pennsylvania State University: 'Aerodynamic Experiments on a Ducted Fan in Hover and Edgewise Flight' http://www.engr.psu.edu/rcoe/theses/Myers_Leighton.pdf
Also: AIAA-98-3116 NASA / TM--1998-208411
General Aviation Light Aircraft Propulsion: From the 1940's to the Next Century Leo A. Burkardt Lewis Research Center, Cleveland, Ohio
Prepared for the 34th Joint Propulsion Conference cosponsored by AIAA, ASME, SAE, and ASEE Cleveland, Ohio, July 12-15, 1998 National Aeronautics and
Space Administration Lewis Research Center, July 1998.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980209647.pdf

It would be helpful to include some of the information from these references to make it more clear what the conclusion is.

Agree with @fooot, we try and stay away from being a link only (or reference only) site.  It's better to pull the relevant information into your answer.

The articles cited have many pages, adding just a few, or some charts, will make losing information. The first image is the basic info, more is available in the links. Thanks for your interesting feedback

A fan is not necessarily a screw, it's any object used to move air towards something. The helix shape happens to be quite ideal but a propeller does not need to be a helix-shaped thing either, just an object used to propel something in a fluid or gas. (Propulsion through a solid is like time traveling: probably impossible. Unless we can imagine something like a tunneler spitting out whatever comes in the other end to move forward.)

Welcome on aviation.SE. You should make some editing effort, use caps at the beginning of sentences and simple dot at the end. You may also enhance your answer by adding references and links for further readings.


text:
Do the A-320 landing gear extend if the mechanism is activated above a limiting speed?
I've been told that on the A-320, if the landing gear lever is lowered with the airspeed above a limiting speed, the system will not extend the landing gear. Further, once the aircraft is slowed to an appropriate speed in this condition (i.e. lever down but wheels up), it is necessary to cycle the landing gear lever up and then back down in order to extend the landing gear.
Can anybody confirm or deny, ideally with a reference, if this description is accurate, and if so, what indications accompany such a lever-down/wheels-up condition.

I overlooked the second part of the question regarding indications, see my extended answer below.

The hydraulic pressure of the landing gear is shut off above 260 KIAS. The maximum gear retraction speed as for the placard in the cockpit is 210 and the max extension speed is 250 KIAS if I'm not mistaken.
From the FCOM 1.32.10
(download from here for example: http://www.smartcockpit.com/plane/AIRBUS/A320.html)
A320 Landing Gear, page 3
OPERATION OF GEAR AND DOORS

NORMAL OPERATION
The green hydraulic system actuates all gear and doors. When the aircraft is flying faster than 260 kt, a safety valve automatically cuts off hydraulic support to the landing gear system. Below 260 kt, the hydraulic supply remains cut off as long as the landing gear lever is up.

The logic is then described in a diagram in the FCOM (see link above).

If ( ADR1 < 260KT || ADR3 < 260KT || MLG on gnd ) && ( LG lever down || safety valve already open )
-> open safety valve

If I interpret this diagram correctly you can leave the gear lever down and the gear should start to extend once below 260 kt because the second side of the and gate just requires the gear lever to be down.
On the contrary if you want to retract the gear and you fly faster than 260 kt then the safety valve closes. Even if you fly slower than 260 kt it will stay closed because the second half of the and gate is not fulfilled. You need to move the gear lever down, then the safety valve opens and then you can move it back up and the self maintained state of "valve already open" will allow you to retract the gear after this cycle of the landing gear lever.
Part 2 of the questions regarding the indications
Indications are as follows:

3 red lights above the gear lever as long as landing gear is not locked in the selected (down) position according to A320 FCOM LANDING GEAR page 18, GEARS AND DOORS, LANDING GEAR INDICATOR PANEL
A red down arrow next to the landing gear lever when the gear is not locked down when the aircraft is in the landing configuration (page 19)
6 red triangles on the ECAM wheel page (3 gears, two redundant landing gear control units) (page 21)
An amber pulsating L/G CTL legend on the ECAM wheels page when the landing gear position and gear position do not agree (page 22)
GPWS audio call out and associated red light outboard of each PFD (see below)
ECAM warnings as follows

ECAM warnings according to the WARNINGS AND CAUTIONS section of the FCOM LANDING GEAR chapter, page 23:

red flashing master warning and cricket aural warning: GEAR NOT DOWNLOCKED on the upper ECAM display, ECAM WHEELs page is called automatically on the lower ECAM display with the indications stated above
red flashing master warning and cricket aural warning: GEAR NOT DOWN, when below 750 ft radar altitude with both engines below 75% N1. Other conditions require flaps to be extended to 3 or FULL but above 260 kt you probably would cause structural damage if you were to attempt that.

From the A320 FCOM Chapter 34 NAVIGATION, GPWS, page 6.

Two aural warnings may be triggered, depending on the area: "TOO LOW-GEAR" [below 190kt and 500ft RA] or "TOO LOW-TERRAIN" [above 190 kt, up to 1000ft RA]

If you are flying faster than 260 kt the GPWS should create a "TOO LOW-TERRAIN" warning.


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How do stealth aircraft reduce the Heat Signature?
According to the wikipedia article, a stealth plane requires the following features in order to reduce its radar signature and thermal detection:

Reducing thermal emission from thrust
Reducing radar detection by altering some general configuration (like introducing the split rudder)
Reducing radar detection when the aircraft opens its weapons bay
Reducing infra-red and radar detection during adverse weather conditions

How do aircraft actually achieve reduction in their thermal emission from thrust?

It helps to realize that IR emissions rise very, very quickly as the temperature rises. 1% of cooling reduces emissions by 4%.

This doesn’t rise to the level of an answer, but one of the greatest defection risks for a low-observability aircraft is not just heat signature, but UV and cosmic radiation silhouetting.  Fairly inexpensive sensors can scan an area of the sky and pick up the random UV scatter pattern caused by the upper atmosphere.  An undetected aircraft passing through the scanned area will cause a silhouette or shadow to the sensor, a small dot where the ambient scatter of the UV energy is blocked by the plane.  There are a lot of detection problems that are really hard to solve.  Even MANPADS use this.

The short of it is that it's really hard to hide the heat signature of a device that is powered by burning large amounts of kerosene and shoving those gases out behind it. IR stealth is therefore a secondary concern (or lower) to designers of stealth fighters, primarily because the IR signature only matters at much closer ranges where stealth technology itself has reduced value (you can hide from radar, and camouflage to an extent, but you can't disappear entirely from visual range).
However, there are some things that can be done to make an aircraft less than blindingly obvious to IR sensors. Here are a few:

High bypass. Not all of the air that enters a turbofan engine's intake enters the actual combustion chamber. Bypass air helps to cool the hot combusted air before it exits, reducing the IR signature.
The A-10, not a "stealth" aircraft in the slightest, nevertheless operates in situations where MANPADS (shoulder-fired SAMs) are a big threat, so to reduce its IR signature it uses some of the highest-bypass turbofans ever put on a military single-seater, at a 6:1 bypass ratio. These high bypass engines, however, reduce performance at high altitudes and high airspeeds; neither disadvantage is a problem for the low, slow A-10's mission profile, but for a more high-performance air superiority fighter this is a big deal.
High-performance jet engines in fighters tend to be relatively low bypass compared to airliner engines for this reason. The F-15 and F-16 were powered by a P&W turbofan with just 0.36:1 bypass ratio, however this only increases IR signature by requiring higher fuel flow rates for the same thrust at lower speeds (lower bypass also reduces the effect of afterburners because there is less unburned bypass air to feed the additional combustion).
The F-22 mitigates the efficiency losses of a turbofan with a variable bypass intake system, allowing it to function as a turbofan with similar bypass to other fighters (about 0.3:1) at low speeds and altitudes, but converting to a near-turbojet configuration (almost zero bypass) at high altitudes and supersonic speeds, which is more fuel-efficient than an afterburner (and so allows the F-22 to supercruise).
Exhaust baffles. The thing designers typically want to avoid at all costs is exposing the actual point of ignition and primary combustion in a jet engine to the ground; this makes the hottest part of a plane's visible IR signature within the plane itself instead of the stream of hot air behind it, allowing easy targeting by IR SAMs. Imagine being an SA-13 "Gopher" mobile SAM launcher and having these twin fireballs from an F-15E for a target:

To hide this massive heat source, stealth aircraft are designed with exhaust vents that mask the exit point of the engine's exhaust from observation by the ground. There's really not a lot you can do design-wise to mask the IR signature from directly behind the aircraft; it's the pilot's job to ensure nobody ends up at that angle within missile range.
Northrop is a fan of directing exhaust out over the top of their fuselage designs. Here's the B-2; you can see the heat plumes of the exhaust trail, but the source of actual combustion is well within the engine housing, and with the aircraft at any altitude the exhaust vent itself would be totally obscured:

Here are the exhaust channels of the YF-23, which incorporated lessons learned from the B-2; notice the similarities in the strategy for directing the exhaust out over the top of the aircraft's trailing edge:

The F-22 Raptor uses a similar theory of tucking the engines way back behind exhaust ducts, but these ducts can move to vector thrust or open to allow afterburners, so for greatest effect the ducts are placed to the rear instead of over the top of the fuselage as Northrop's designs tend to:

EMR-absorbing materials. A basic part of stealth design is the use of materials that absorb radar, and designing the aircraft's surfaces with angles that minimize the number of surfaces providing a direct return at any angle, while remaining aerodynamic. Other materials can absorb other frequencies in the EMR spectrum including IR; the Space Shuttle's lower and leading surfaces were covered in special ceramic tiles that could absorb enormous amounts of thermal energy while being cool to the touch. A similar material, not quite as effective but also less delicate, is used to protect the exhaust ducts of stealth fighters, and this has a secondary effect of lowering the radiant heat signature of the engines because the exhaust nozzles stay cooler. The radar absorbing material used elsewhere has some capacity for absorbing heat on leading edges, which helps avoid good lock-on by all-aspect IR missiles, but it's not the material's primary job.

In summary, designers do try to minimize IR signature, but tactically, if an enemy can launch an IR missile at you you have already failed at being stealthy. An infrared missile launch requires the launcher to tell the missile where to look, and that means they must at least be able to look at you themselves (using helmet-cued AA missiles), if not point the missile itself or the tracking radar at you. The idea of stealth is to minimize the amount of time the enemy knows that you exist by being invisible on radar, so they can't see you coming until they spot you visually, at which point they're either already dead or have mere seconds to react. Then for a ground run it's "one pass and haul ass" to avoid reprisals from anti-aircraft systems, while for an air-to-air engagement the first plane to launch a missile has an extreme advantage (and thus the advantage starts with the first plane to know where the other one is).

The 2nd paragraph of your High Bypass section would make an excellent answer to the supercruise question.

@FreeMan - It already is :-)

oh... Well done, mate!!!

"and with the aircraft at any altitude the exhaust vent itself would be totally obscured"  ...unless the attacker is, I don't know, another aircraft.

You forgot something: injecting cooling agents into the exhaust. The F-117 did that, probably others as well as needed.

While they try to reduce it as best they can its often low on the list,
According to this article

The SR-71 was designed to minimize its radar cross-section, an early attempt at stealth design.[21] Finished aircraft were painted a dark blue, almost black, to increase the emission of internal heat

One of the problems you get at is that airframes heat up at high speeds. In the case of the blackbird it was fast enough (and could fly high enough) to outrun anything anyway so heat signature was less of a concern.
According to this article

In the B-2, all of the exhaust passes through cooling vents before flowing out of the rear ports

So it seems they cool the exhaust. Im not sure what effects this has on the over all thrust that the plane generates but Im sure it has an effect in some way.
The article also goes on to talk about the exhaust placement and how top mounted exhaust can help with ground based sensing that is looking up at the bottom of the craft

Putting the exhaust ports on the top of the plane further reduces the infrared signature, since enemy sensors would most likely scan below the plane.

Reducing heat signature has 2 main functions. To keep the plane from showing up on ground based heat sensing systems and to keep thermal guided weapons from locking on. For what its worth the SR-71 was able to outrun most missiles of the time, some 4000 by all accounts.
For what its worth:

the SR-71 design did not take into account the extremely hot engine exhaust and the particles in the hot exhaust reflect radar extremely well. Ironically, the SR-71 was one of the largest targets on the FAA (Federal Aviation Administration) long range radars, which were able to track the plane at several hundred miles

So arguably the greatest spy plane of all time was not even that stealthy...
In regards to the F-117

exhaust was channeled through long narrow ducts lined with heat-absorbing material so that it was cooler by the time it exited the plane and therefore did not show up as well on heat detectors

Seems similar to the system employed on the B2

Low observable aircraft are designed to emit IR radiation at frequencies that are less useful for sensors and/or better absorbed by the atmosphere.  This is done with coatings.  Some aircraft such as the F-35 also use heat exchangers put some of the heat generated into the fuel supply.  Heat sources such as the radar can be cooled by fuel rather than allowing the heat to escape the the atmosphere.


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Help me understand the A220-100 takeoff chart
Here is the takeoff performance chart of the Airbus A220 (CS100). According to Wikipedia, the MTOW runway length needed is 1500 metres. However, this chart seems to suggest that a runway length of almost 2500 metres would be required for an A220-100 operating at MTOW weight.
Am I reading the chart incorrectly?

A220-100 Airport planning guide page 57/190 for the graph
A220 Wikipedia specs

Done! Thanks for the suggestion

Performance is all dependent upon aircraft gross takeoff weight, runway conditions (e.g. surface type, gradient, etc.), ambient winds and density altitude at the airfield.  There is no one required length of runway needed to depart. That all has to be calculated prior to departure, and ensure that the runway available can accommodate the airplane.
Assuming the data above is correct for the purposes in question, I would start from the horizontal axis, then draw a vertical line up from the aircraft’s gross takeoff weight to the pressure altitude at the airfield, thence a horizontal line going left from that point to the vertical axis, which will give you your takeoff field length.


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Airship design principles
Close your eyes for a second, and try to imagine you're designing this new generation Airship.

The above diagram is a simple sketch to bring it to life and make it more realistic.

Key

Blue ellipse represents the balloon inflated with Hydrogen or Helium
Gray rectangular box on top of the balloon is something like a solar panel or a cover plain object material.
Yellow boxes represent propellers used to steer this Airship.
Dark red rectangular object below the blue balloon is the payload.

Question
Assuming the blue balloon is inflated with enough gas to lift the total weight of this Airship. Am wondering whether this Airship would withstand harsh windy conditions due to it's payload, a colleague told me i'd add holes in between the payload object or make the payload object flexible in the way that it can swing freely from the balloon.
This got me so confused. Am also interested in learning best practices for designing less bumpy airships that can withstand harsh conditions.

That airship is going to catch wind really easily.

@SMSvonderTann what would be the best way to achieve this, a long-height payload Airship

Basically you have a large sail hanging from the bottom of the airship. You can calculate the wind loading on this, but since it is hanging from the airship it will create a rolling moment. It will also act as a giant rudder if its thin as you show.

I am not really experienced with this, but something more "fat" and torpedo-like would work better. Also, I can't help but notice that the airship looks like Dory.

@RonBeyer I do understand the wind that fall onto it, my goal is to have a thin payload but with a more longer height, not used as a rudder

This might be relevant: Lockheed Martin Hybrid Airship

Whether or not you want to use it as one, it is one. This thing will windvane unless you have very powerful engines to hold it against the wind. Even then, you're going to drift if you can hold heading.

@SMSvonderTann Nice one :) it does look like Dory.... Anyway so you mean i should convert the rectangular payload to torpedo-like in  a way that this Airship has two ellipse-shaped objects?

Welcome! Your question is more suited for a discussion in the chatroom than for direct answers, as many questions come to mind when looking at your design. So you are welcome to start a thread.

With a lighter-than-air craft, a primary consideration is to encapsulate the most volume with the smallest amount of material.  This creates the best lift-to-weight ratio. A sphere is ideal, and you see nearly sphere-like shapes in weather balloons, hot air balloons and blimps.
While your side-view looks circular, it is clear from your top and cross-sectional view that there is actually very little volume, relative to the surface area of your balloon.   This just won't hold much H or He relative to all the fabric needed.
So aside from weather-vaning problems (after all, you could only fly in calm conditions), this thing is just too inefficient.

My diagram above is just a sketch, the balloon is supposed to be fat and big in the side-ways, i.e it can hold much H or He. My main goal is to have a long-height payload, i think you haven't talked about it in your answer

Look, your sketch is what you gave us, and all we have to work with.  You cannot give us a poor diagram, ask us for comments, and then deny our comments because you provided a bad diagram.

I think i have just told you that it's just a simple diagram (don't mind about the proportion)

The proportion is critical.  Proportions are what drives aircraft design.  Without proportion, all airplanes are just "two wings and a body... don't worry about the sizes"

You're right about that, all i wanted was to give out a simple picture of what this airship would be like, it's something rough i did in Libreoffice.

If you want good answers, you have to provide good information.  GIGO


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How do I calculate fuel reserves for IFR and VFR flight plan?
I am trying to figure out how to calculate for IFR and VFR for a flight plan example. So from my basic understanding, VFR means you have to add extra 30 minutes to your fuel reserve, and 45 minutes for IFR. So if I wanted to make a flight plan, would I do distance/speed + .5 (for VFR) or + .75 (for IFR)? For instance, if I am calculating that I need an hour's worth of fuel to go a distance of 100 miles at 100 MPH, how would I figure out how much fuel I'd need taking VFR/IFR into consideration?

Its not that simple. Its 30 minutes for daytime VFR, or 45 minutes for night time. For IFR, you need to be able to fly to your destination, your alternate, and for 45 minutes beyond that, unless weather is above certain minimums. See 14 CFR 91.167 for IFR and 14 CFR 91.151 for VFR, assuming this is FAA (US regulations).

And for knowing how much fuel to take into consideration, this is simply looking at the cruise performance charts for that particular aircraft and finding the amount of gallons per hour based on the altitude and power setting. For 30 minutes you take half that value, for 45 minutes you take 75% of that value. You really can't calculate how much fuel you need without knowing how much you are burning. Ground distance really doesn't have anything to do with it, other than calculating how much you need to get from dest->alternate, but you also need to know the wind for that.

For FAA regulations:
Once you've gotten everything planned and it's time to add on the fuel reserve, it is based on the airplane's fuel burn rate from a regulatory standpoint.
If the airplane burns ten gallons per hour, you can easily calculate that you need an extra five gallons, which is 30 minutes of flight duration at ten gallons per hour, for day VFR, and you would need 7.5 for night VFR under FAA regulations, which is 45 minutes of duration, so you would just add those to the total that you calculated that you would need to get to your destination, and you have successfully planned your reserve.
For IFR, you would have to select an alternate if the weather conditions require one, plan your flight to your destination, then to the alternate, and then add on 45 minutes worth of fuel after reaching the alternate, which would be 7.5 gallons after reaching the alternate airport.
This is the regulation for IFR reserve: 91.167


text:
How does one determine the freestream and ultimate slipstream velocities to estimate thrust?
The task before me is estimating the thrust of a propulsion system (a ducted fan) using this equation for thrust (Eq. 2.1.1)1:
$$T = (mass\; flow\; rate)\;(slipstream\; velocity - freestream\; velocity) $$
I know what the ideal inlet and exit velocities of the system are, but how does one determine the freestream and slipsteam velocities so that estimated thrust may be calculated?

1 Warren F. Phillips, Mechanics Of Flight Second Edition, John Wiley & Sons, Inc., Hoboken, New Jersey, 2010, p.153

The free stream velocity can be measured with a calibrated air data system. This uses a pitot tube somewhere at the front, the readings of which have been compared to known speeds in previous flights. The difference between the total pressure and the static pressure gives the dynamic pressure which can be translated into the desired speed.
The speed in the slipstream must be measured across the full cross section to ensure that the full speed profile is known so the slipstream speed used for thrust calculation really is the mean of all the speeds in the slipstream. This is done by measuring the total pressure at several locations, for example by using a moveable rake.

Combined temperature and pressure rake (picture source)

Thanks, Peter. It occurred to me that I could also check the text I cited for "freestream velocity".

If I had, I would have seen on the second page of the text: "...V∞ is the freestream velocity or  relative wind far from the body...". So, for estimating static thrust, I could use zero.

@DavidWalden: That is correct, however, some formulas put the free stream velocity in the denominator, so setting this to zero might not always be the easy solution it seems.


text:
What is this orange container labeled "Flight kit wheel"?
What is this orange container for?
It reads

Flight kit wheel. Do not remove.

What's a "flight kit wheel"?

The most important question, and the one we've all overlooked for 2 years - "Why have they removed it from the plane???" ;)

@FreeMan We all silently asked this one :)

Short answer
Corsair is a small airline, with a limited number of aircraft, serving airports in remote islands from Paris. For their economical survival their aircraft must keep a high operational ratio. However:

The airline may not have a maintenance facility at destination, either a owned facility or an agreement for maintenance services from another company locally based.

The facility may not have a satisfactory stock of spare parts for their aircraft or the required tools, and no possibility to obtain them in a very short time, even from their main base.

A common solution is to bring parts aboard, in particular MEL components. It's a balance between the cost to carry the container and the cost of extra wait time (better said by FreeMan in a comment below: The weight penalty is much lower than the wait penalty.)
These containers marked Flight kit, Fly away kit (FAK), Do not unload, Do not offload, etc, contain components or tools intended to remain on board and be used at the next stopover in case of necessity.
It's relatively common to see FAK for spare wheels. One of the reasons is when the crew executes a rejected take-off just prior to V1 speed on a large aircraft, brakes are subject to intense heating propagated to the wheels. Tires inflated with nitrogen at about 1,300 kPa (that's about 13 bars or 200 psi) could blow out beyond a certain temperature, causing damages/injuries. To prevent such explosion, wheels are fitted with fusible plugs melting to allow tires to deflate safely.
After such event, the plugs (and possibly the tire) have to be replaced. A common option is to change the whole wheel and perform inspection and repairs later. The kit contains the necessary tooling and parts for this replacement. This might take 30 minutes or so.
As FreeMan also mentions, sometimes the mechanic who is going to replace the wheel is onboard. That was the case (at the time the photo was shot) for Corsair for certain destinations where there is no permanent maintenance team at the stopover.
Corsair, a small airline serving remote locations
And actually Corsair is a small French airline based at Paris-Orly (LFPO), which has a taste of holidays. Their 5 aircraft take people from Paris to beautiful beaches on islands where airports don't have large maintenance facilities (Fort-de-France, Pointe-à-Pitre, La Réunion, Saint Martin, Palma ...)
For a long time Corsair used Boeing 747 Classic, meaning also less common spare parts.
In such a small airline, when an aircraft is grounded the schedule of the others is indeed disrupted, the shorter, the better.
Flight kit

Loading a flight kit, source Linde

Flight kit, Air France (translates to "Fly away kit, do not unload"). Photo by A380spotter at Flickr

Flight kit wheels in cargo hold (Malawi elections inspection). Source
Secured content
Parts in the container are secured to prevent them from moving.

AKN FSK container for Air France (Source)

(source)
See also: Do any aircraft carry spare parts for making repairs?

Corsair, formerly Corse Air, comes from Corse island (the birth place of Napoleon Bonaparte). Their business has known ups and downs several times, they are now part of Dubreuil Group. Corsair 747 had over time famous tail numbers: F-GSEA, F-GSEX, F-GSUN, F-GSKY, F-HLOV, etc.

F-GSEA landing at Princess Juliana. Source: JetPhotos, photo by Rogier van der Velde

Great answer! I didn't know that airliners were actually flying with a spare wheel (or whatever other spare part), due to the weight penalty.

@QuentinHayot The weight penalty is much lower than the wait penalty, therefore, it makes sense to have parts on board. It would be interesting to find out if Corsair flies mechanics aboard every time, or if they have/contract them locally when needed.

Wow I love the term "wait penalty"

I was working on a project 15 years ago where we were negotiating with an airline to use one of their B737s to obtain an STC. They quoted the cost (in 2002) to pull the aircraft out of service at $70k/day.

@FreeMan: Corsair had at the time some maintenance facilities (the main being at Orly), and at small locations, a mechanic was following the aircraft, as stated by one of those mechanics here (in Fr): "I followed the planes to the stopovers where there was no maintenance (CORSAIR stopover or service provider) to be able to do the maintenance of the planes."

Does "following" the aircraft mean the mechanic rode on board most/all flights? To me, "following" means to come after (like take the next flight). Probably just a Frenglish translation issue...

@Freeman, In french it's also a bit ambiguous, but the most probable meaning is "I was onboard". But it's also possible the mechanics stays at the stopover for some days, before returning to Paris and being replaced by a colleague.

Fair enough, thanks for the clarification! (I also envisioned the mechanic "following" the aircraft on a tether, like a towed banner, but I was pretty sure that wasn't it, either. :)


text:
Who has the final authority over sidesticks?
I’m wondering what would happen if - for some reason - the pilot and his copilot were fighting over the control of an Airbus with their respective sidesticks.
Does the pilot gets the final word ? Does it works like in a traditional system, where the strongest one takes it all, but through force feedback ?

Possible duplicate of Why is the Priority Takeover button used?

@user71659 related, but what if both priority takeover buttons are pressed at the same time ?

Possible duplicate of Why do Airbus sidesticks add their inputs?

If they were fighting, intentionally attempting to gain control over the stick, the pilot pressing the last would win. This differs from the situation in a cockpit with coupled controls, where the pilot who pushes hardest wins. So in an Airbus, a quick pilot wins from a strong pilot..
From the FCTM:

When the Pilot Flying (PF) makes an input on the sidestick, an order (an electrical signal) is sent to the fly-by-wire computer. If the Pilot Not Flying (PNF) also acts on the stick, then both signals/orders are added.
Therefore, as on any other aircraft type, PF and PNF must not act on their sidesticks at the same time. If the PNF (or Training Captain) needs to take over, the PNF must press the sidestick priority pushbutton, and announce: "I have control".
If a flight crewmember falls on a sidestick, or a mechanical failure leads to a jammed stick (there is no associate ECAM caution), the "failed" sidestick order is added to the "non failed" sidestick order.
In this case, the other not affected flight crewmember must press the sidestick priority pushbutton for at least 40 seconds, in order to deactivate the "failed" sidestick.
A pilot can at any time reactivate a deactivated stick by momentarily pressing the takeover push button on either stick.

Flight International featured an article on the A320 on 30 August 1986. It discusses the sidesticks, which were new for civil aviation at the time, and an Airbus representative makes an interesting point:

"If sidesticks were the normal way for flying aircraft, no one would even consider changing to a control column that makes it difficult for the pilot to get into his seat and which blocks his view of the instrument panel when he's there.."

It is really hard to find an unassociated person though, who is of opinion that uncoupled sticks are better than coupled sticks.

There was an study which showed that dual input incident rates were the same on Boeing as Airbus aircraft. Dual input incidents are instinctive/panic reaction on both, the PM just grabs without thinking.  And the pilot acts as an internal servo loop, you push to what you think is the right position. When you encounter resistance, your first instinct is to push even harder. In both cases, a uncontrolled input occurs. At least with the Airbus, you can lock out the other pilot if you hit the button. It's easy to blame the new system when it's the pilot's problem.

@user71659 Agreed, and I totally agree that both systems are very safe and sensible. Only stating that the Airbus sticks would be the best of all worlds if all features are retained as is, plus mechanical coupling is added so that a panicking pilot is made aware of conflicting inputs via the force sensors in his fingers.


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What is the maximum pitch for the Boeing 787 Dreamliner?
I recently watched a video of the Boeing 787 training before Farnborough.  This aircraft climbed very fast; does someone know the maximum pitch of this aircraft?

30 degrees.
Boeing aircraft, including the 787, have a Pitch Limit Indicator (PLI) in the flight display that tells the pilot how far the wing's angle of attack (AOA) is from stall.

the PLI also is limited to 30 deg of pitch attitude, regardless of AOA.

But it depends on aircraft configuration

During takeoff climb, there is no single target AOA to fly that will guarantee certified takeoff performance. Takeoff-climb AOA will vary with such factors as airplane gross weight, thrust, altitude, flap setting, and CG. Takeoff-climb speeds (hence, AOA) are limited by stall speed, tail clearance, and minimum control speeds. The higher speed and greater thrust of an all-engine takeoff reduce the AOA significantly relative to an engine-out takeoff at the engine-out climb speed (V2 ).

From Boeing Aero No.12

At Farnborough 2014, pilots Neville and Bryan were pulling stunts that would get airline pilots fired. Most airlines limit pitch to 20 degrees (or in a few cases 25) from what I've read.

They kicked off the demonstration with a spectacularly steep takeoff, pitching the plane up just shy of 30 degrees.

I'd guess they flew just inside what Boeing consider unsafe for those conditions.

Boeing won’t reveal ... just how steeply it can take off

From Wired - "terrifying" (my emphasis).
I think we can be reasonably confident that no production 787 will ever, after take-off, initially climb at greater than 30 degrees.

Flight envelopes
The way I understand it, asking about the "maximum" of anything for an aircraft is less useful than understanding the flight envelope. This is because the maximum depends very greatly on the exact situation of the aircraft including things like altitude, weight, speed etc.

Actual flight data from the six Boeing 787 test aircraft.

Ok, the aircraft speed depend of Altitude, Engines and all of this stuff.
But the conditions of the demonstation, I think, was : Takeoff in Farnborough (238 ft) at maximum power of Engines, and an aircraft without interior.
See the demonstration here

@Kromen: From that angle it looked more dramatic than it actually was. See updated answer ...

Thank you, obliviously is not considered as safe takeoff but it's very spectacular.


text:
What causes harsh noise during TX/RX on VHF radio?
I am running some trial radio test on PAE VHF main radio and during TX from ATC there is harsh noise at the background even though TX is 5/5. Likewise for the incoming RX from aircrafts. So I swapped the main radio with the standby radio but is giving me same results. I want to know what is causing this noise and how to eliminate it.

Apart from the fact that you're using ATC transmissions, this doesn't seem to be an aviation question. You might do better on [electronics.se]

Noise on comms is a common aviation problem @ReddHerring, and for me it's on topic.

@GdD "on topic" is defined by what is written here https://aviation.stackexchange.com/help/on-topic and not what someone thinks might be remotely on topic. If that were the case this place would be a madhouse. :) This is an electronics/communications issue with VHF radios of any kind, not an aviation-specific issue.

@JuanJimenez There are VHF, UHF and HF radios on board of aircraft. There are also hydraulic systems and electrical systems on board of aircraft. While hydraulics, electricity and radio transmission are all part of physics, they are part of aviation as well.

@Koyovis The scope of this site does not cover hydraulics, electricity or radio transmission. This one is about specific subjects in aviation and there are other StackExchange sites that can address those subjects. If you don't agree you can always submit a proposal to change the statement of scope.

@JuanJimenez You may consult posts like this ome.

By "harsh noise" do you mean white noise or some other type of noise, like crackling, etc?

This would be closed as off topic if posted on Electrical Engineering SE as it is a usage or repair question and not a design question.  Look for local issues, for example if the noise correlates with the engine being on/off and RPM it could be a problem with noisy power.  If the source were external and in-band, a handheld or radios in another aircraft adjacent on the ramp would experience it, too.  If both radios are of the same design its vaguely possible some extremely strong out of band transmission could exploit a susceptibility in the architecture of both.

If the transmit signal is strong the Signal-to-Noise Ratio is high, which would mean that the noise that you hear is not background white noise filtered through the VHF frequency band. First thing I would look for is an active noise transmitter on the band, which would only be present in a limited set of frequencies.
Hard to say from behind the keyboard what causes the noise that you hear, suggestions for troubleshooting:

Is the noise present at all Xmit frequencies?
Does it diminish if you move away from your present position?
Does your squelch setting help at all?

In fairness, the received signal can be strong while the S/N ratio is low. This can happen, for example, if you have a high noise floor where the receiver is located. The transmitted power would seem to have little bearing here, except that with a high transmit power, you'd be able to reach farther before the S/N ratio drops to any given value with any given noise power at the receiver location.

Indeed, this answer fundamentally misunderstands the term "Signal-to-Noise Ratio" - the intent might have been to suggest that the AGC would have ramped down the gain.